Vehicles recently having advanced functions include various rotation angle detectors detects steering wheels of the vehicles for executing various controlling.
FIG. 11 is a perspective view of an essential part of a conventional rotation angle detector. Spur gear 1A is provided on a rim of rotor 1, and fitting part 1B for fitting to a shaft of a steering wheel (not shown) passing through rotor 1 is provided inside rotor 1. Spur gear 2A on a rim of detecting element 2 engages with spur gear 1A of rotor 1, and magnet 3 is mounted at the center of detecting element 2 preferably by insert molding. Wiring board 4 is provided on a top face of detecting element 2 substantially in parallel to detecting element 2. Wiring board 4 has wiring patterns (not illustrated) formed on both faces thereof. Magnetic sensor 5 mounted on wiring board 4 faces magnet 3 of detecting element 2. Magnet 3 and magnetic sensor 5 facing each other composes detecting unit 6. Control unit 7 connected to magnetic sensor 5 is provided on wiring board 4 preferably as a microcomputer. The control unit is connected to an electronic circuit (not illustrated) in the vehicle with a connector (not illustrated), thus providing a rotation angle detector.
When the steering wheel rotates, rotor 1 rotates, and accordingly, detecting element 2 including spur gear 2A engaged to spur gear 1A on the rim of rotor 1 rotates. According to the rotation of detecting element 2, a magnetic field from magnet 3 mounted at the center of detecting element 2 changes. Magnetic sensor 5 detects the magnetic intensity, and outputs a detection signal having a substantially triangular waveform to control unit 7. Then, control unit 7 detects the rotation angle of rotor 1 based on the number of peaks of the waveform and a level of the detection signal received from magnetic sensor 5.
In the conventional detector, the rotation angle of rotor 1 is detected by single detecting element 2 engaged to rotor 1. This arrangement causes the detector not to detect the rotation angle accurately if detecting element 2 detaches from rotor 1 or if spur gear 2A is damaged or worn.
Japanese Patent Laid-Open Publication No.2002-206910 discloses another conventional rotation angle detector.